Our prior research on Pavlovian aversive (Av) to instrumental appetitive (Ap) transfer showed that a danger signal (AvCS plus) contingent upon the food-reinforced response in a visual choice discrimination facilitated learning whereas a safety signal (AvCS minus) retarded learning. These and related findings suggested that a CS functioned to signal the presence (CS plus) or absence (CS minus) of one type of affective event (e.g., Av) and that such a function readily transferred to a qualitatively different (e.g., Ap) reinforcer. Subsequent investigations of the mediational properties of the CSs indicated, however, that our findings were better interpreted as across-reinforcement blocking effects: A response-contigent AvCS minus or AvCS plus, by signaling a preferred or a non-preferred outcome (absence or presence of shock), produced little if any or a large positive discrepancy with the preferred outcome of food reinforcement and thereby blocked or counterblocked (enhanced) the association of reinforcement and the Sd. This blocking interpretation has been supported by studies investigating (1) Ap to Ap transfer in the same discrimination-learning paradigm and (2) Ap to Av transfer in a conditioned-suppression paradigm. Our current research is investigating factors controlling these within and across-reinforcement blocking effects and the specific interpretations which may account for them. Assessment focuses on (1) qualitative and quantitative variations in the reinforcers (Ap or Av) employed, (2) the kinds of learning processes that can be affected, e.g., conditioning-extinction and excitatory-inhibitory processes, and (3) the nature of the compounds, e.g., simultaneous or sequential, used to generate blocking effects in both Pavlovian and instrumental/operant tasks. The latter includes investigation of response-reinforcer relationships where, in the absence of discriminative control, the instrumental response may itself be blocked or counterblocked by a contingent CS.